Short-term effects of polyethene and polypropylene microplastics on soil phosphorus and nitrogen availability

Microplastics alter the microbiota-mediated phosphorus profiles at sediment-water interface: Distinct microbial effects between sediment and plastisphere

Microplastics (MPs) are ubiquitous in freshwater sediments, raising concern about their potential impacts on ecosystem services. However, the specific impacts of microbiota mediated by MPs in sediment and plastisphere compartments on P availability remain elusive. This investigation conducted a series of microcosm experiments utilizing eutrophic lake sediment amended with fuel-based polyethylene terephthalate (PET), bio-based polylactic acid (PLA) MPs, and a natural cobblestone substrate to unravel their effects. The findings highlighted that MPs induced alterations in bacterial communities in both sediment and plastisphere, consequently modifying P availabilities at the sediment-water interface (SWI). In comparison to non-biodegradable PET, biodegradable PLA MPs presented higher proportions of specific bacteria and functional genes associated with P profiles, such as Firmicutes, Ignavibacteriota, and P mineralizing genes in the sediment and plastisphere. This, in turn, elevated the levels of soluble reactive P in the porewater by 54.19 % (0-1 cm), 55.81 % (1-3 cm), and 18.24 % (3-5 cm), respectively. Additionally, PLA obviously altered P immobilization capacity and bioavailability, increasing the organic P fraction. Whereas, inert cobblestone exhibited negligible influence on P biogeochemical processes during the incubation. Moreover, the biofilm communities and those in the surrounding sediment specifically contributed to the changes in P profiles at the SWI. The functional genes associated with P profiles in the sediment mainly concentrate on P mineralization and P uptake/transport. In the plastisphere, P activation genes are obviously affected under MP exposure. This study fills the knowledge gap concerning the repercussions of MPs on ecosystem services.

The microplastics distribution characteristics and their impact on soil physicochemical properties and bacterial communities in food legumes farmland in northern China

Microplastics (MPs) pose a threat to farmland soil quality and crop safety. MPs exist widely in food legumes farmland soil due to the extensive use of agricultural film and organic fertilizer, but their distribution characteristics and their impact on soil environment have not been reported. The abundance and characteristics of MPs, soil physical and chemical properties, and bacterial community composition were investigated in 76 soil samples from five provinces in northern China. The results showed that the abundance of MPs ranged from 1600 to 36,200 items/kg. MPs in soil were mostly fibrous, less than 0.2 mm, and white. Rayon, polyester and polyethylene were the main types of MPs. The influences of MPs on soil physicochemical properties and bacterial communities mainly depended on the type of MPs. Notably, polyethylene significantly decreased the proportion of silt particles, and increased the nitrate nitrogen content as well as the abundance of MPs-degrading bacteria Paenibacillus (p < 0.05). Moreover, bacteria were more sensitive to polyesters in soil with low concentration of organic matter. This study indicated that MPs in food legumes farmland soil presented a higher-level. And, they partially altered soil physicochemical properties, and soil bacteria especially in soil with low organic matter.

Effects of combined microplastics and heavy metals pollution on terrestrial plants and rhizosphere environment: A review

Microplastics (MPs) can enter the soil environment through industry, agricultural production and daily life sources. Their interaction with heavy metals (HMs) poses a significant threat to a variety of terrestrial ecosystems, including agricultural ones, thereby affecting crop quality and threatening human health. This review initially addresses the impact of single and combined contamination with MPs and HMs on soil environment, including changes in soil physicochemical properties, microbial community structure and diversity, fertility, enzyme activity and resistance genes, as well as alterations in heavy metal speciation. The article further explores the effects of this pollution on the growth characteristics of terrestrial plants, such as plant biomass, antioxidant systems, metabolites and photosynthesis. In general, the combined contaminants tend to significantly affect soil environment and terrestrial plant growth, i.e., the impact of combined contaminants on plants weight ranged from -87.5% to 4.55%. Similarities and differences in contamination impact levels stem from the variations in contaminant types, sizes and doses of contaminants and the specific plant growth environments. In addition, MPs can not only infiltrate plants directly, but also significantly affect the accumulation of HMs in terrestrial plants. The heavy metals concentration in plants under the treatment of MPs were 70.26%-36.80%. The co-occurrence of these two pollution types can pose a serious threat to crop productivity and safety. Finally, this study proposes suggestions for future research aiming to address current gaps in knowledge, raises awareness about the impact of combined MPs + HMs pollution on plant growth and eco-environmental security.

Microplastic coupled with soil dissolved organic matter mediated changes in the soil chemical and microbial characteristics

The abundance of microplastics (MPs) in soil environments has attracted significant attentions, due to their impact on soil physico-chemical properties. However, limited information is available on the influences of MPs on soil carbon composition and microbial utilization characteristics. Therefore, a two-month incubation experiment was conducted to add polyethylene microplastics (PE-MPs) with different levels (1%, 10%) and sizes (150-300 μm and 75-150 μm) into different soils. After that, soil chemical properties including the dissolved organic carbon (DOC), spectral characteristics of dissolved organic matter (DOM) and soil microbial characteristics were analyzed. Results revealed that PE-MPs addition caused significant differences in soil chemical properties between farmland and woodland soils, particularly in soil pH, DOM composition, and soil phosphatase activity. Woodland soil always exhibited higher levels of DOC content, microbial diversity, and soil carbon source utilization compared to farmland soil, leading to increased humification in the DOM of woodland soil. PE-MPs with a larger particle size significantly increased both the soil DOC content and enzyme activity. Addition of PE-MPs altered the soil DOM composition, and the fluorescence parameters like the biological index (BIX) and humification degree. Moreover, the carbon source utilization intensity of microorganisms on PE MPs-contaminated soils is higher in woodland soils. Various analyses confirmed that compared to other soil properties, characteristics of soil DOM had a more significant impact on soil microbial community composition. Thus, PE-MPs in conjunction with soil DOM spectral characteristics regulated soil microbial diversity, which is crucial for understanding soil carbon sequestration.

Effects of microplastics on soil microorganisms and microbial functions in nutrients and carbon cycling - A review

The harmful effects of microplastics (MPs) pollution in the soil ecosystem have drawn global attention in recent years. This paper critically reviews the effects of MPs on soil microbial diversity and functions in relation to nutrients and carbon cycling. Reports suggested that both plastisphere (MP-microbe consortium) and MP-contaminated soils had distinct and lower microbial diversity than that of non-contaminated soils. Alteration in soil physicochemical properties and microbial interactions within the plastisphere facilitated the enrichment of plastic-degrading microorganisms, including those involved in carbon (C) and nutrient cycling. MPs conferred a significant increase in the relative abundance of soil nitrogen (N)-fixing and phosphorus (P)-solubilizing bacteria, while decreased the abundance of soil nitrifiers and ammonia oxidisers. Depending on soil types, MPs increased bioavailable N and P contents and nitrous oxide emission in some instances. Furthermore, MPs regulated soil microbial functional activities owing to the combined toxicity of organic and inorganic contaminants derived from MPs and contaminants frequently encountered in the soil environment. However, a thorough understanding of the interactions among soil microorganisms, MPs and other contaminants still needs to develop. Since currently available reports are mostly based on short-term laboratory experiments, field investigations are needed to assess the long-term impact of MPs (at environmentally relevant concentration) on soil microorganisms and their functions under different soil types and agro-climatic conditions.

Microplastics affect the ecological stoichiometry of plant, soil and microbes in a greenhouse vegetable system

Microplastic (MP) pollution is a growing global issue due to its potential threat to ecosystem and human health. Low-density polyethylene (LDPE) MP is the most common type of plastics polluting agricultural soils, negatively affecting soil-microbial-plant systems. However, the effects of LDPE MPs on the carbon (C): nitrogen (N): phosphorus (P) of soil-microbial-plant systems have not been well elucidated. Thus, we conducted a pot experiment with varying LDPE MP concentrations (w/w) (control without MPs; 0.2 % MPs (PE1); 5 % MPs (PE2); and 10 % MPs (PE3)) to study their effects on soil-microbial-plant C-N-P stoichiometry. Soil C:N ratio increased 2.3 and 3.4 times in PE2 and PE3, respectively. Soil C:P ratio increased 2.2 and 3.6 times in PE2 and PE3, respectively. Soil microbial C:N ratios decreased by 46.2 % in PE1, while C:P ratios decreased by 59.2, 38.6, and 67.9 % in PE1, PE2, and PE3, respectively. Soil microbial N:P ratio decreased in PE1 (17.2) and PE3 (59.1 %). MPs increased shoot C content and C:N ratios, particularly at the 5 % MP addition rate. MP addition altered dissolved organic C, N, and P concentrations, depending on the MP addition rate. Microbial community responses to MP exposure were complex, leading to variable effects on different microbial groups at different MP addition rates. Structural equation modeling showed that MP addition had a direct positive effect (β = 0.96) on soil C-N-P stoichiometry and a direct negative effect (β = -1.34) on microbial C-N-P stoichiometry. These findings demonstrate the complex interactions between MPs, soil microorganisms, and nutrient dynamics, highlighting the need for further research to better understand the ecological implications of MP pollution in terrestrial ecosystems.

The impact of arbuscular mycorrhizal fungi and endophytic bacteria on peanuts under the combined pollution of cadmium and microplastics

It remains unclear how symbiotic microbes impact the growth of peanuts when they are exposed to the pollutants cadmium (Cd) and microplastics (MPs) simultaneously. This study aimed to investigate the effects of endophytic bacteria Bacillus velezens SC60 and arbuscular mycorrhizal fungus Rhizophagus irregularis on peanut growth and rhizosphere microbial communities in the presence of Cd at 40 (Cd40) or 80 (Cd80) mg kg-1 combined without MP or the presence of low-density polyethylene (LDPE) and poly butyleneadipate-co-terephthalate (PBAT). This study assessed soil indicators, plant parameters, and Cd accumulation indicators. Results showed that the application of R. irregularis and B. velezens significantly enhanced soil organic carbon and increased Cd content under the conditions of Cd80 and MPs co-pollution. R. irregularis and B. velezens treatment increased peanut absorption and the enrichment coefficient for Cd, with predominate concentrations localized in the peanut roots, especially under combined pollution by Cd and MPs. Under treatments with Cd40 and Cd80 combined with PBAT pollution, soil microbes Proteobacteria exhibited a higher relative abundance, while Actinobacteria showed a higher relative abundance under treatments with Cd40 and Cd80 combined with LDPE pollution. In conclusion, under the combined pollution conditions of MPs and Cd, the co-treatment of R. irregularis and B. velezens effectively immobilized Cd in peanut roots, impeding its translocation to the shoot.

Microplastics enhance the invasion of exotic submerged macrophytes by mediating plant functional traits, sediment properties, and microbial communities

Plant invasions and microplastics (MPs) have significantly altered the structure and function of aquatic habitats worldwide, resulting in severe damage to aquatic ecosystem health. However, the effects of MPs on plant invasion and the underlying mechanisms remain largely unknown. In this study, we conducted mesocosm experiments over a 90-day period to assess the effects of polystyrene microplastics on the invasion of exotic submerged macrophytes, sediment physicochemical properties, and sediment bacterial communities. Our results showed that PS-MPs significantly promoted the performance of functional traits and the invasive ability of exotic submerged macrophytes, while native plants remained unaffected. Moreover, PS-MPs addition significantly decreased sediment pH while increasing sediment carbon and nitrogen content. Additionally, MPs increased the diversity of sediment bacterial community but inhibited its structural stability, thereby impacting sediment bacterial multifunctionality to varying degrees. Importantly, we identified sediment properties, bacterial composition, and bacterial multifunctionality as key mediators that greatly enhance the invasion of exotic submerged macrophytes. These findings provide compelling evidence that the increase in MPs may exacerbate the invasion risk of exotic submerged macrophytes through multiple pathways. Overall, this study enhances our understanding of the ecological impacts of MPs on aquatic plant invasion and the health of aquatic ecosystems.

Short-term impacts of polyethylene and polyacrylonitrile microplastics on soil physicochemical properties and microbial activity of a marine terrace environment in maritime Antarctica

Evidence of microplastic (MP) pollution in Antarctic terrestrial environments reinforces concerns about its potential impacts on soil, which plays a major role in ecological processes at ice-free areas. We investigated the effects of two common MP types on soil physicochemical properties and microbial responses of a marine terrace from Fildes Peninsula (King George Island, Antarctica). Soils were treated with polyethylene (PE) fragments and polyacrylonitrile (PAN) fibers at environmentally relevant doses (from 0.001% to 1% w w-1), in addition to a control treatment (0% w w-1), for 22 days in a pot incubation experiment under natural field conditions. The short-term impacts of MPs on soil physical, chemical and microbial attributes seem interrelated and were affected by both MP dose and type. The highest PAN fiber dose (0.1%) increased macro and total porosity, but decreased soil bulk density compared to control, whereas PE fragments treatments did not affect soil porosity. Soil respiration increased with increasing doses of PAN fibers reflecting impacts on physical properties. Both types of MPs increased microbial activity (fluorescein diacetate hydrolysis), decreased the cation exchange capacity but, especially PE fragments, increased Na+ saturation. The highest dose of PAN fibers and PE fragments increased total nitrogen and total organic carbon, respectively, and both decreased the soil pH. We discussed potential causes for our findings in this initial assessment and addressed the need for further research considering the complexity of environmental factors to better understand the cumulative impacts of MP pollution in Antarctic soil environments.

First national reference of microplastic contamination of French soils

The recent emergence of studies on plastic contamination of terrestrial environments has revealed the presence of microplastics (MP) in a variety of soil types, from the most densely populated areas to the most remote ones. However, the concentrations and chemical natures of MP in soils vary between studies, and only a few ones have focused on this issue in France. The MICROSOF project aimed to establish the first national references for French soil contamination by microplastics. 33 soil samples randomly chosen on the French soil quality-monitoring network were analyzed. The study collected data on the abundance of microplastics in the [315-5000] μm range, their chemical nature and size, as well as mass abundance estimates and other relevant information. Results demonstrated that 76 % of the soil samples contained microplastics, in concentrations ranging from <6.7 to 80 MP.kg-1 (dry soil). Most samples from croplands, grasslands and vineyards and orchards were contaminated, whereas only one sample from forest contained MP, suggesting an increased risk of microplastic contamination in soils exposed to agricultural practices. The MP abundances are not statistically different from similar studies, indicating an intermediate level of contamination in French soils. Despite intervention reports and surveys, the sources remain unclear at this stage. For the first time, an overview of the state of soil contamination in France, as well as the potential risks is provided.

The impacts of microplastics on the cycling of carbon and nitrogen in terrestrial soil ecosystems: Progress and prospects

As contaminants of emerging concern, microplastics (MPs) are ubiquitously present in almost all environmental compartments of the earth, with terrestrial soil ecosystems as the major sink for these contaminants. The accumulation of MPs in the soil can trigger a wide range of effects on soil physical, chemical, and microbial properties, which may in turn cause alterations in the biogeochemical processes of some key elements, such as carbon and nitrogen. Until recently, the effects of MPs on the cycling of carbon and nitrogen in terrestrial soil ecosystems have yet to be fully understood, which necessitates a review to summarize the current research progress and propose suggestions for future studies. The presence of MPs can affect the contents and forms of soil carbon and nitrogen nutrients (e.g., total and dissolved organic carbon, dissolved organic nitrogen, NH4+-N, and NO3--N) and the emissions of CH4, CO2, and N2O by altering soil microbial communities, functional gene expressions, and enzyme activities. Exposure to MPs can also affect plant growth and physiological processes, consequently influencing carbon fixation and nitrogen uptake. Specific effects of MPs on carbon and nitrogen cycling and the associated microbial parameters can vary considerably with MP properties (e.g., dose, polymer type, size, shape, and aging status) and soil types, while the mechanisms of interaction between MPs and soil microbes remain unclear. More comprehensive studies are needed to narrow the current knowledge gaps.

Phosphorus fertiliser application mitigates the negative effects of microplastic on soil microbes and rice growth

Soil microplastics (MPs) have attracted widespread attention recently. Most studies have explored how soil MPs affect the soil's physicochemical parameters, matter circulation, and soil microbial community assembly. Similarly, a key concern in agricultural development has been the use of phosphorus (P) fertiliser, which is essential for plant health and development. However, the relationship between MPs and phosphate fertilisers and their effects on the soil environment and plant growth remains elusive. This study assessed the influence of adding low-density polyethylene MPs (1%) with different phosphate fertiliser application rates on microbial communities and rice biomass. Our results showed that MPs changed the structure of soil bacterial and phoD-harbouring microbial communities in the treatment with P fertiliser at the same level and suppressed the interactions of phoD-harbouring microorganisms. In addition, we found that MPs contamination inhibited rice growth; however, the inclusion of P fertiliser in MP-contaminated soils reduced the inhibitory action of MPs on rice growth, probably because the presence with P fertiliser promoted the uptake of NO3--N by rice in MP-contaminated soils. Our results provide further insights into guiding agricultural production, improving agricultural management, and rationally applying phosphate fertilisers in the context of widespread MPs pollution and global P resource constraints.

Biodegradable PBAT microplastics adversely affect pakchoi (Brassica chinensis L.) growth and the rhizosphere ecology: Focusing on rhizosphere microbial community composition, element metabolic potential, and root exudates

Biodegradable plastics (BPs) have gained increased attention as a promising solution to plastics pollution problem. However, BPs often exhibited limited in situ biodegradation in the soil environment, so they may also release microplastics (MPs) into soils just like conventional non-degradable plastics. Therefore, it is necessary to evaluate the impacts of biodegradable MPs (BMPs) on soil ecosystem. Here, we explored the effects of biodegradable poly(butylene adipate-co-terephthalate) (PBAT) MPs and conventional polyethylene (PE) MPs on soil-plant (pakchoi) system at three doses (0.02 %, 0.2 %, and 2 %, w/w). Results showed that PBAT MPs reduced plant growth in a dose-dependent pattern, while PE MPs exhibited no significant phytotoxicity. High-dose PBAT MPs negatively affected the rhizosphere soil nutrient availability, e.g., decreased available phosphorus and available potassium. Metagenomics analysis revealed that PBAT MPs caused more serious interference with the rhizosphere microbial community composition and function than PE MPs. In particular, compared with PE MPs, PBAT MPs induced greater changes in functional potential of carbon, nitrogen, phosphorus, and sulfur cycles, which may lead to alterations in soil biogeochemical processes and ecological functions. Moreover, untargeted metabolomics showed that PBAT MPs and PE MPs differentially affect plant root exudates. Mantel tests, correlation analysis, and partial least squares path model analysis showed that changes in plant growth and root exudates were significantly correlated with soil properties and rhizosphere microbiome driven by the MPs-rhizosphere interactions. This work improves our knowledge of how biodegradable and conventional non-degradable MPs affect plant growth and the rhizosphere ecology, highlighting that BMPs might pose greater threat to soil ecosystems than non-degradable MPs.

Dose-Dependent Effects of a Corn Starch-Based Bioplastic on Basil (Ocimum basilicum L.): Implications for Growth, Biochemical Parameters, and Nutrient Content

Plastic pollution is a pressing global issue, prompting the exploration of sustainable alternatives such as bioplastics (BPs). In agriculture, BPs have gained relevance as mulching films. This study investigated the effect of the presence in the soil of different concentrations (0-3%, w/w) of a corn starch-based bioplastic on basil (Ocimum basilicum L.). The results showed that increasing bioplastic concentration reduced shoot fresh biomass production. Biochemical analyses revealed changes in the shoot in soluble protein content, biomarkers of oxidative and osmotic stress (malondialdehyde and proline, respectively), anti-radical activity, and antioxidant compounds (phenols, flavonoids, and ascorbic acid), which are indicative of plant adaptive mechanisms in response to stress caused by the presence of the different concentrations of bioplastic in the soil. Macro- and micronutrient analysis showed imbalances in nutrient uptake, with a decreased content of potassium, phosphorus, and manganese, and an increased content of magnesium, iron, and copper in the shoot at high BP concentrations.

Machine learning prediction and interpretation of the impact of microplastics on soil properties

The annual microplastic (MP) release into soils is 4-23 times higher than that into oceans, significantly impacting soil quality. However, the mechanisms underlying how MPs impact soil properties remain largely unknown. Soil-MP interactions are complex because of soil heterogeneity and varying MP properties. This lack of understanding was exacerbated by the diverse experimental conditions and soil types used in this study. Predicting changes in soil properties in the presence of MPs is challenging, laborious, and time-consuming. To address these issues, machine learning was applied to fit datasets from peer-reviewed publications to predict and interpret how MPs influence soil properties, including pH, dissolved organic carbon (DOC), total P, NO3--N, NH4+-N, and acid phosphatase enzyme activity (acid P). Among the developed models, the gradient boost regression (GBR) model showed the highest R2 (0.86-0.99) compared to the decision tree and random forest models. The GBR model interpretation showed that MP properties contributed more than 50% to altering the acid P and NO3--N concentrations in soils, whereas they had a negligible impact on total P and 10-20% impact on soil pH, DOC, and NH4+-N. Specifically, the size of MPs was the dominant factor influencing acid P (89.3%), pH (71.6%), and DOC (44.5%) in soils. NO3--N was mainly affected by the MP type (52.0%). The NH4+-N was mainly affected by the MP dose (46.8%). The quantitative insights into the impact of MPs on soil properties of this study could aid in understanding the roles of MPs in soil systems.

Study on the mechanism of co-pyrolysed biochar on soil DOM evolution in short-term cabbage waste decomposition

Cabbage waste returned soil was studied to assess the short-term influences of the application of cabbage waste biochar (CB), pine wood biochar (PB), and co-pyrolysed biochar (PCB) on soil dissolved organic matter (DOM) evolution. The decrease in DOM and soil organic matter (SOM) content was greater in the biochar-added soils during 35 days of decomposition. The DOM and SOM content in PCB added group decreased by 26.96 mg L-1 and 4.48 g kg-1, respectively. The increase in relative abundance of humic acid-like substances in DOMs was higher in the biochar-added soils during decomposition, which increased by 4.29% in PCB added group. PCB addition also resulted in a high SOM content (initial content of 78.82 g kg-1), and mineral elements were introduced into the soil, thus increasing soil pH (7.81) and electrical conductivity (574.67 μs cm-1). Moreover, the addition of biochars attenuated the decrease in average relative abundance of Bacillaceae and promoted bacterial proliferation during decomposition. The application of biochars regulated the soil bacterial community and promoted organic matter conversion and soil DOM evolution.

Accessing the intrinsic factors of carbonyl index of microplastics: Physical and spectral properties, baseline correction, calculation methods, and their interdependence

Carbonyl index (CI) is a measure of the degradation status of microplastics. While many studies address environmental factors of microplastic degradation, intrinsic factors like physical properties, spectral properties, baseline correction, and CI calculation methods are less explored. This research focused on these aspects using surface seawater samples. We found that color and shape have limited dependence on particle size or signal-to-noise ratio (SNR). Baseline correction can significantly alter CI values, with the direction of the shift depending on the methods used. Additionally, most CI values before and after baseline correction and those calculated using different methods tend to be strongly correlated. Using the selected CI calculation methods, we found that CI values varied significantly by shape and color. CI's relation to the similarity between the sample and its pristine form suggests an alternative degradation measure. Our findings emphasize the need for standardized CI calculation methods.

Effects of micro(nano)plastics on soil nutrient cycling: State of the knowledge

The ecological impacts of micro(nano)plastics (MNPs) have attracted attention worldwide because of their global occurrence, persistence, and environmental risks. Increasing evidence shows that MNPs can affect soil nutrient cycling, but the latest advances on this topic have not systematically reviewed. Here, we aim to present the state of knowledge about the effects of MNPs on soil nutrient cycling, particularly of C, N, and P. Using the latest data, the present review mainly focuses on three aspects, including (1) the effects and underlying mechanisms of MNPs on soil nutrient cycling, particularly of C, N and P, (2) the factors influencing the effects of MNPs on soil nutrient cycling, and (3) the knowledge gaps and future directions. We conclude that MNPs can alter soil nutrient cycling via mediating soil nutrient availability, soil enzyme activities, functional microbial communities, and their potential ecological functions. Furthermore, the effects of MNPs vary with MNPs characteristics (i.e., polymeric type, size, dosage, and shape), chemical additives, soil physicochemical conditions, and soil biota. Considering the complexity of MNP-soil interactions, multi-scale experiments using environmental relevant MNPs are required to shed light on the effects of MNPs on soil nutrients. By learning how MNPs influence soil nutrients cycles, this review can guide policy and management decisions to safeguard soil health and ensure sustainable agriculture and land use practices.

Polyethylene microplastic and soil nitrogen dynamics: Unraveling the links between functional genes, microbial communities, and transformation processes

Microplastics (MPs) have emerged as pollutants of growing concern due to their potential threat to soil ecosystems. While some studies have investigated the effects of MPs on soil nitrogen content, the underlying physicochemical and microbial driving mechanisms still need to be explored. In this study, a six-month incubation experiment was conducted with varying polyethylene MP addition rates: CK (0%, mass ratio), MP0.5 (0.5%), MP1 (1%), MP2 (2%), MP4 (4%), and MP8 (8%). The experiment aimed to examine the effects of MPs on soil nitrogen content, physicochemical properties, nitrogen cycling-related genes, microorganisms, and gross nitrogen transformation rates. The results revealed no significant changes in soil total nitrogen and dissolved total nitrogen. However, dissolved organic nitrogen significantly decreased by 16.00-54.60% following MP addition, while ammonium (NH4+-N, 45.71-271.43%) and nitrate (NO3--N, 43.15-209.54%) nitrogen and microbial biomass nitrogen (46.02-123.70%) significantly increased. Soil pH, bulk density, and soil porosity decreased after MP addition, while soil carbon contents, water-stable macroaggregates, and redox potential increased. The soil microbial community structure changed significantly, and microbial diversity increased under MP treatment. MP addition significantly altered the abundance of soil nitrogen cycling functional genes. The relative abundance of nitrogen fixation and denitrification genes decreased with increasing MP addition rates, while organic degradation and synthesis genes increased. The soil nitrogen cycling functional microbial composition shifted dramatically with increased MP addition. Networks with high addition rates (MP2 +MP4 +MP8) exhibited more total nodes, total links, negative links, node degrees, and modules but shorter average path distances and lower modularity than those with low addition rates (CK +MP0.5 +MP1), reflecting increased network complexity induced by MPs. The gross ammonification rate, NH4+-N consumption and immobilization rates, and NO3--N immobilization rate increased, while the gross nitrification rate and net nitrification rate exhibited an initial increase followed by a decrease with increasing MP addition rates, peaking at MP2. Furthermore, redundancy analysis and structural equation modeling demonstrated that soil physicochemical properties significantly affected soil nitrogen cycling genes and microorganisms, ultimately altering nitrogen content. In conclusion, polyethylene MPs promoted soil nitrogen mineralization and transformation and changed the related functional microorganism community structure, exhibiting a noticeable dose-effect relationship. This study provides deeper insight into the effects of MPs on soil nitrogen cycling.

Effects of complex pollution by microplastics and heavy metals on soil physicochemical properties and microbial communities under alternate wetting and drying conditions

Microplastics (MPs) broadly coexist with heavy metals (HMs) in soil, Cd and Cu are the main types of soil HMs contamination, in addition to polystyrene (PS), which is also widely present in the environment and prone to aging. However, differences in the effects of MPs and HMs on soil properties and microbial characteristics under alternating wetting and drying (AWD) remain unclear. Thus, this study investigated the effects of four conventional (0.2% (w/w)) and aged MPs in indoor incubation experiments on soil properties under desiccation (Dry) and AWD. We found that with the influence of the "enzyme lock" theory, the coexistence of MPs and HMs under Dry had a more pronounced effect on soil physicochemical properties, whereas the effects on soil enzyme activity under AWD were more significant. In addition, MPs decreased the available Cu by 4.27% and, conversely, increased the available Cd by 8.55%. Under Dry, MPs affected microbial function mainly through physicochemical properties, with a contribution of approximately 72.4%, whereas under AWD enzyme activity and HMs were significantly greater, with increases of 28.2% and 7.9%, respectively. These results indicate that the effects of MPs on environmental variation and microbial profiles under AWD conditions differed significantly from those under Dry.

Challenges of Raman spectra to estimate carbonyl index of microplastics: A case study with environmental samples from sea surface

This study investigates the feasibility of using the carbonyl index (CI) derived from Raman spectra as an indicator of plastic degradation and its relationship with the CI calculated from Fourier transform infrared (FTIR) spectra, using microplastic samples of polyethylene (PE) from surface seawater. Multiple methods were used to calculate the CI values of FTIR spectra, while proposed methods were used to calculate the corresponding CI values of Raman spectra. Some significant relations between FTIR CI and Raman CI were observed. However, small R2 values suggest weak functional relationships, which can be attributed to the low signal-to-noise ratio (SNR) of Raman spectra. These results highlight the challenges of establishing a functional relationship between FTIR CI and Raman CI, including challenges such as the uniformity of Raman spectra, determining optimal Raman measurement parameters, selecting appropriate peaks for Raman CI calculation, deciding on spectral processing methods, and addressing the interdependence of these issues.

Polyethylene and polyvinyl chloride microplastics promote soil nitrification and alter the composition of key nitrogen functional bacterial groups

Microplastics (MPs) contamination in soils seriously threatens agroecosystems globally. However, very few studies have been done on the effects of MPs on the soil nitrogen cycle and related functional microorganisms. To assess MP's impact on the soil nitrogen cycle and related functional bacteria, we carried out a one-month soil incubation experiment using typical acidic soil. The soil was amended with alfalfa meal and was spiked with 1% and 5% (mass percentage) of low-density polyethylene (LDPE) and polyvinyl chloride (PVC) MPs. Our results showed that both LDPE and PVC addition significantly increased soil nitrification rate and nitrate reductase activity, which could further promote soil denitrification. The relative abundance of diazotrophs, ammonium oxidizing, and denitrifying bacterial groups were significantly altered with MPs addition. Moreover, the MPs treatments greatly enhanced denitrifying bacteria richness. Redundancy analysis showed that nitrate reductase activity was the most significant factor affecting the soil functional bacterial community. Correlation analysis shows that Nitrosospira genus might be for the improvement of soil nitrification rate. Our results implied that MPs exposure could significantly affect the soil nitrogen cycling in farmland ecosystems by influencing essential nitrogen functional microorganisms and related enzymatic activities.

Long-term microbial community succession and mechanisms of regulation of dissolved organic matter derivation in livestock manure fermentation system

Industrial-scale aerobic fermentation was conducted with livestock manures. Microbial inoculation promoted the growth of Bacillaceae and consolidated its position as the dominant microorganism. Microbial inoculation substantially influenced dissolved organic matter (DOM) derivation and variations of related components in the fermentation system. The relative abundance of humic acid-like substances of DOM increased from 52.19% to 78.27% in microbial inoculation system, resulting in a high humification level. Moreover, lignocellulose degradation and microbial utilization were the important factors influencing DOM content in fermentation systems. The fermentation system was regulated by microbial inoculation, thus achieving a high level of fermentation maturity.

Microplastics change the leaching of nitrogen and potassium in Mollisols

Nowadays, the dynamics of nutrients leaching from the soils and their driving mechanism have been focused on, however, it is still unclear how microplastics (MPs) influence the nutrients' leaching in soils. In this study, five concentrations (w/w, 0.0 %, 0.5 %, 1 %, 2 %, 3 %) and three sizes of MPs of polyethylene (PE) (0.15-0.36 mm, 0.36-0.60 mm and 0.60-1.00 mm) influencing the leaching of NO₃^--N and water-soluble potassium (WSK) was simulated by a column method in Mollisols, and both the pre-fertilization and post-fertilization were considered. The results showed that, before KNO₃ addition, there was a negative power function relationship between the NO₃^--N concentration and the leaching solution volume/leaching time. The amount and concentration of NO₃^--N leaching was higher in the early leaching stage. Compared with the CK, PE_0.5% significantly reduced the leaching amount of WSK, while increased the leaching amount of NO₃^--N but not significantly. The leaching amount of WSK decreased with the increasing size of PEMP when the PEMP concentration was the same, while NO₃^--N was opposite. PE_0.60-1.00 increased the leaching amount of NO₃^--N, while reduced the leaching amount of WSK. After KNO₃ addition, compared with CK, PE_1% significantly reduced the leaching amount of NO₃^--N, and PE_1% had the lowest leaching amount of WSK. However, when the PEMP concentration in the soil reached a certain threshold (w/w, >1 %), the leaching amount of NO₃^--N and WSK increased gradually with PEMP increasing. PE_0.60-1.00 reduced the leaching amount of NO₃^--N and WSK most obviously. In general, low concentrations (w/w, <1 %) and large sizes (0.60-1.00 mm) of PEMP promoted NO₃^--N leaching and inhibited the WSK leaching from the soil before the addition of KNO₃, however, they both inhibited the leaching of NO₃^--N and WSK from the soil after addition of KNO₃.

Concurrence of microplastics and heat waves reduces rice yields and disturbs the agroecosystem nitrogen cycle

Microplastic pollution and heat waves, as damaging aspects of human activities, have been found to affect crop production and nitrogen (N) cycling in agroecosystems. However, the impacts of the combination of heat waves and microplastics on crop production and quality have not been analyzed. We found that heat waves or microplastics alone had slight effects on rice physiological parameters and soil microbial communities. However, under heat wave conditions, the typical low-density polyethylene (LDPE) and polylactic acid (PLA) microplastics decreased the rice yields by 32.1% and 32.9%, decreased the grain protein level by 4.5% and 2.8%, and decreased the lysine level by 91.1% and 63.6%, respectively. In the presence of heat waves, microplastics increased the allocation and assimilation of N in roots and stems but decreased those in leaves, which resulted in a reduction in photosynthesis. In soil, the concurrence of microplastics and heat waves induced the leaching of microplastics, which resulted in decreased microbial N functionality and disturbed N metabolism. In summary, heat waves amplified the disturbance induced by microplastics on the agroecosystem N cycle and therefore exacerbated the decreases in rice yield and nutrients induced by microplastics, which indicates that the environmental and food risks of microplastics deserve to be reconsidered.

Impacts of microplastics and heavy metals on the earthworm Eisenia fetida and on soil organic carbon, nitrogen, and phosphorus

Microplastics (MPs) are increasingly being studied because they have become ubiquitous in aquatic and terrestrial environments. However, little is known about the negative effects of co-contamination by polypropylene microplastic (PP MPs) and heavy metal mixtures on terrestrial environment and biota. This study assessed the adverse effects of co-exposure to PP MPs and heavy metal mixture (Cu²⁺, Cr⁶⁺, and Zn²⁺) on soil quality and the earthworm Eisenia fetida. Soil samples were collected in the Dong Cao catchment, near Hanoi, Vietnam, and analyzed for changes in extracellular enzyme activity and carbon, nitrogen, and phosphorus availability in the soil. We determined the survival rate of earthworms Eisenia fetida that had ingested MPs and two doses of heavy metals (the environmental level - 1 × - and its double - 2 ×). Earthworm ingestion rates were not significantly impacted by the exposure conditions, but the mortality rate for the 2 × exposure conditions was 100%. Metal-associated PP MPs stimulated the activities of β-glucosidase, β-N-acetyl glucosaminidase, and phosphatase enzymes in soil. Principle component analysis showed that these enzymes were positively correlated with Cu²⁺ and Cr⁶⁺ concentrations, but negatively correlated with microbial activity. Zn²⁺ showed no correlation with soil extracellular enzyme activity or soil microbial activity. Our results showed that co-exposure of earthworms to MPs and heavy metals had no impact on soil nitrogen and phosphorus but caused a decrease in total soil carbon content, with a possible associated risk of increased CO₂ emissions.

A first report on the spatial and temporal variability of microplastics in coastal soils of an urban town in south-western India: Pre- and post-COVID scenario

We present a first study on the temporal changes (2019-2021) in the microplastic abundance in the coastal soils of an urban town in the south-western part of India. All sampling stations exhibited higher abundances of microplastics in soils collected during 2021 (959.7 ± 277.7 particles/kg) compared to those collected in 2019 (515.1 ± 182.7 particles/kg). Morphologically, flakes, fibres, and films are the most abundant types documented in the soil environment. The microplastics of 0.3-5 mm size are relatively more abundant (60.6 %) compared to those of 0.03-0.3 mm size (39.4 %) in 2021. The three main types of polymers (polypropylene and high- and low-density polyethylene) in the soil exhibited an increase in abundance during an interval of 15 months (October 2019 to March 2021). In addition to packaging materials, the enhanced use of surgical masks during the COVID-19 period might have acted as a source of microplastic contamination in the soils.

Potential impact of polyethylene microplastics on the growth of water spinach (Ipomoea aquatica F.): Endophyte and rhizosphere effects

Microplastic contamination has received much attention, especially in agroecosystems. However, since edible crops with different genetic backgrounds may present different responses to microplastics, more research should be conducted and focused on more edible crops. In the current study, pot experiments were conducted to investigate the potential impact of polyethylene microplastic (PE) (particle sizes: 0.5 μm and 1.0 μm, addition levels: 0 (control), 0.5% and 1.0% (w/w)) addition on the physiological and biochemical variations of I. aquatica F.. The results indicated that PE addition caused an increase in the soil pH and NH₄⁺-N and soil organic matter contents, which increased by 10.1%, 29.9% and 50.1% when PE addition at A10P0.5 level (10 g (PE) kg^-1 soil, particle size: 0.5 μm). While, PE exposure resulted in a decrease in soil available phosphorus and total phosphorus contents, which decreased by 53.9% and 10.5% when PE addition at A10P0.5 level. In addition, PE addition altered the soil enzyme activities. Two-way ANOVA indicated that particle size had a greater impact on the variations in soil properties and enzyme activities than the addition level. PE addition had a strong impact on the rhizosphere microbial and root endophyte community diversity and structure of I. aquatica F.. Two-way ANOVA results indicated that the particle size and addition level significantly altered the α-diversity indices of both rhizosphere microbial and root endophyte (P < 0.05, P < 0.01 or P < 0.001). Moreover, PE was adsorbed by I. aquatica F., which was clearly observed in the transverse roots and significantly increased the H₂O₂, ·O₂^-, malondialdehyde and ascorbic acid contents in both the roots and aerial parts of I. aquatica F., leading to a decrease in I. aquatica F. biomass. Overall, the current study enriches the understanding of the effect of microplastics on edible crops.

Global meta-analysis reveals differential effects of microplastics on soil ecosystem

A large number of individual studies and meta-analyses have shown that microplastics (MPs) affect soil ecosystems. However, the effects of different concentrations and types of MPs on soil ecosystem are still unclear. Here, a comprehensive meta-analysis was performed to examine the responses of 19 variables, associated with soil properties, microbes, enzymes, and fauna, to MPs, based on 114 peer-reviewed studies. The results showed that the addition of MPs significantly reduced the soil organic carbon (SOC), total nitrogen (TN), NH₄⁺-N, pH, and diversity of bacteria, and increased the dissolved organic carbon (DOC), diversity of fungi and enzyme activities, especially enzymes related to the biogeochemical cycle. We further discussed that soil MPs exerted negative effects on soil fauna, including survival, growth, and reproduction, and that the concentration of MPs, rather than the type, was the biggest driving factor causing the toxicity of MPs affecting soil animals. More importantly, the concentrations of MPs were the main factor affecting the DOC, TN, NO₃^--N, total phosphorus (TP), available phosphorus (AP), and diversity of fungi, whereas the types of MPs were the main factors reflected in the SOC, NH₄⁺-N, pH, diversity of bacteria, and enzyme activities. This study aimed to evaluate the response of soil ecosystems to the different concentrations and types of MPs, and the largest driving factor for the toxicity of MPs.

Ignoring the Effects of Photovoltaic Array Deployment on Greenhouse Gas Emissions May Lead to Overestimation of the Contribution of Photovoltaic Power Generation to Greenhouse Gas Reduction

Photovoltaic (PV) power generation is one of the world's most promising options for carbon emission reduction. However, whether the operation period of solar parks can increase greenhouse gas (GHG) emissions in hosting natural ecosystems has not been fully considered. Here, we conducted a field experiment to compensate for the lack of evaluation of the effects of PV array deployment on GHG emissions. Our results show that the PV arrays caused significant differences in air microclimate, soil properties, and vegetation characteristics. Simultaneously, PV arrays had more significant effects on CO₂ and N₂O emissions but a minor impact on CH₄ uptake in the growing season. Of all the environmental variables included, soil temperature and moisture were the main drivers of GHG flux variation. The sustained flux global warming potential from the PV arrays significantly increased by 8.14% compared to the ambient grassland. Our evaluation models identified that the GHG footprint of PV arrays during the operation period on grasslands was 20.62 g CO₂-eq kW h^-1. Compared with our model estimates, GHG footprint estimates reported in previous studies were generally less by 25.46-50.76%. The contribution of PV power generation to GHG reduction may be overestimated without considering the impact of PV arrays on hosting ecosystems.

Microplastics in terrestrial ecosystem: Sources and migration in soil environment

Plastics, especially microplastics in soils, are considered a severe environmental issue worldwide. However, globally, the main research focus is on microplastic pollution in the marine environment, the microplastic pollution on soils and sediments remains on the sideline so far. But the fact is that microplastics are omnipresent in terrestrial systems in the form of microbeads in industrial systems and in sewage sludge. Their presence in agricultural soils and sediments is enormously increased due to plastic mulching, plastic greenhouses and compost and extensive use of controlled release fertilizers. Therefore, this review outlines the global scenario regarding plastics and microplastics production, consumption, and possible pathways of penetration into the soil environment. Various mechanisms to restrict and manage the pathways of plastics and microplastics into the soil environment are also discussed. This review also focuses on the challenges and limitations on the use of plastic alternates such as bioplastics and oxo plastics. Also, the knowledge gaps on the source of microplastics in the environment and their deleterious effects on properties of soil, soil health and focused light on their soil trophic transfer in food chains via plants. This review provides a detailed insight on the management and possible control measures to alleviate the potential risk caused by microplastics pollution in the soil environment and the overall ecosystem's health. In spite of the occurrence and fate of microplastics on terrestrial environment, knowledge gaps and challenges for tackling this contamination are also explored which facilitates the policy makers to develop regulatory measures towards the containment of microplastics in living ecosystem.

Effects of microplastics on nitrogen and phosphorus cycles and microbial communities in sediments

Sediments are the long-term sinks of microplastics (MPs) and nutrients in freshwater ecosystems. Therefore, understanding the effect of MPs on sediment nutrients is crucial. However, few studies have discussed the effects of MPs on nitrogen and phosphorus cycles in freshwater sediments. Herein, 0.5% (w/w) polyvinyl chloride (PVC), polylactic acid (PLA), and polypropylene (PP) MPs were added to freshwater sediments to evaluate their effects on microbial communities and nitrogen and phosphorus release. The potential biochemical functions of the bacterial communities in the sediments were predicted and assessed via 16S rRNA gene sequencing. The results showed that MPs significantly affected the microbial community composition and nutrient cycling in the sediments. PVC and PP MPs can promote microbial nitrification and nitrite oxidation, while PP can significantly promote alkaline phosphatase (ALP) activity and the abundance of the phosphorus-regulation (phoR) gene. PLA MPs had the potential to promote the abundance of microbial phosphorus transporter (ugpB), nitrogen fixation (nifD, nifH, and nifX), and denitrification (nirS, napA, and norB) genes and inhibit nitrification, resulting in massive accumulation and release of ammonia nitrogen. Although PLA MPs inhibited the activity of ALP and the abundance of the organophosphorus mineralization (phoD) gene, it could enhance dissimilatory iron and sulfite reduction, which may promote the release of sedimentary phosphorus. Our findings may help understand the mechanisms of nitrogen and phosphorus cycles and microbial communities driven by MPs in sediments and provide a basis for future assessments of the environmental behavior of MPs in freshwater ecosystems.

Effects of microplastics on cadmium accumulation by rice and arbuscular mycorrhizal fungal communities in cadmium-contaminated soil

Both microplastics (MPs) and cadmium (Cd) are common contaminants in soil-rice systems, but their combined effects remain unknown. Thereby, we explored the effects of three MPs, i.e., polyethylene terephthalate (PET), polylactic acid (PLA), and polyester (PES), on Cd accumulation in rice and the community diversity and structure of arbuscular mycorrhizal fungi (AMF) in soil spiked with or without Cd. Results showed that 2% PLA decreased shoot biomass (-28%), but PET had a weaker inhibitive effect. Overall, Cd alone did not significantly change shoot and root biomass and increased root biomass in combination with 0.2% PES. MPs generally increased soil Cd availability but decreased Cd accumulation in rice tissues. Both MPs and Cd improved the bioavailability and uptake of Fe and Mn in rice roots. MPs altered the diversity and community composition of AMF, depending on their type and dose and co-existing Cd. Overall, 2% PLA caused the most distinct changes in soil properties, plant growth and Cd accumulation, and AMF communities, but showed no synergistic interactions with Cd. In conclusion, MPs can mediate rice performance and Cd accumulation via altering soil properties, nutrient uptake, and root mycorrhizal communities, and biodegradable PLA MPs thought environment-friendly can exhibit higher phytotoxicity than conventional MPs.

Microplastics Derived from Food Packaging Waste-Their Origin and Health Risks

Plastics are commonly used for packaging in the food industry. The most popular thermoplastic materials that have found such applications are polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET), and polystyrene (PS). Unfortunately, most plastic packaging is disposable. As a consequence, significant amounts of waste are generated, entering the environment, and undergoing degradation processes. They can occur under the influence of mechanical forces, temperature, light, chemical, and biological factors. These factors can present synergistic or antagonistic effects. As a result of their action, microplastics are formed, which can undergo further fragmentation and decomposition into small-molecule compounds. During the degradation process, various additives used at the plastics' processing stage can also be released. Both microplastics and additives can negatively affect human and animal health. Determination of the negative consequences of microplastics on the environment and health is not possible without knowing the course of degradation processes of packaging waste and their products. In this article, we present the sources of microplastics, the causes and places of their formation, the transport of such particles, the degradation of plastics most often used in the production of packaging for food storage, the factors affecting the said process, and its effects.

Role of polyamide microplastic in altering microbial consortium and carbon and nitrogen cycles in a simulated agricultural soil microcosm

Microplastics (MPs) are persistent organic pollutants globally, with a continuous increase in MP wastes near and away from the regions of human activities. Studies to date aimed to explore the impact of MPs on ecosystems, but the area of research could not go beyond environmental pollution caused by MPs. To address the menace of MPs, scientists need to pay enough attention to the biogeochemical cycles, microbial communities, and functional microorganisms. Hence, this study aimed to evaluate the impact of adding 0.3% (mass ratio) [low-concentration (LC) group] and 1% [high-concentration (HC) group] of polyamide (PA) MP to the soil microenvironment with regard to the aforementioned parameters. PA MP decreased the soil microbial diversity (Shannon and Simpson indices, P < 0.05). At the phylum level, PA MP increased the abundance of Acidobacteria, Firmicutes, and Crenarchaeota (P < 0.05); at the genus level, it enhanced that of Geobacter, Thiobacillus, Pseudomonas, and Bradyrhizobium (P < 0.01) while decreased that of Bacillus, Flavisolibacter, Geothrix, and Pseudarthrobacter (P < 0.05). PA MP affected the carbon (C) cycle. PA MP accelerated the soil C fixation by enhancing the abundance of the genes accA and pccA. The LC PA MP accelerated organic C degradation and methane metabolism by changing the abundance of mnp, chiA, mcrA, pmoA, and mmoX genes, while the HC PA MP inhibited them with increasing the experimental time. Regarding the effects of PA on the nitrogen (N) cycle, the PA MP promoted N assimilation and ammonification by increasing the abundance of the genes gdh and ureC, the impact of PA MP on N fixation and denitrification depended on its concentration and treating time. This study showed that PA MP impacted the microbial consortium, it also affected the C and N cycles and its effect depended on its concentration and the treating time.

Effects of solution chemistry and humic acid on transport and deposition of aged microplastics in unsaturated porous media

Microplastics (MPs) are susceptible to aging in the environment, and aged MPs are highly migratory in soil due to their smaller particle size and more negative surface charge, but the effects of soil environmental factors on the fate and transport of aged MPs are still unclear. In this study, the transport behavior of pristine/aged MPs in unsaturated sandy porous media was examined under different ionic strength (IS), cationic type (Na⁺, Ca²⁺) and humic acid (HA) conditions. The results indicated that the surface charge, surface oxygen-containing functional groups and surface morphology of MPs changed significantly after aging, and that the mobility of aged MPs was significantly enhanced than the pristine MPs under all test conditions. The retention amounts of pristine/aged MPs in unsaturated porous media increased with IS, and IS had a less inhibitory effect on the transport of aged MPs than pristine MPs. The mobility of pristine/aged MPs in Ca²⁺ solutions was significantly weaker than that in Na⁺ solutions due to enhanced straining and electrostatic adsorption. HA promoted the mobility of pristine/aged MPs in unsaturated porous media under all IS Na⁺ (1, 10, and 25 mM) solutions and lower IS (1 mM) Ca²⁺ solutions, and the ability of HA to promote the transport of aged MPs was significantly stronger than that of pristine MPs due to the higher adsorption of HA on the surface of aged MPs. However, at higher IS (10 mM) Ca²⁺ solution conditions, the bridging effect of Ca²⁺ led to the formation of HA-MPs complexes, which altered the hydrophobicity of the pristine/aged MPs surface and the pristine/aged MPs were mainly retained on the air-water interface (AWI). CFT theory and two-site kinetic retention models indicated that the retention of pristine/aged MPs in unsaturated media was dominated by monolayer adsorption, straining and clogging effects. The current research findings may provide insights into the fate and transport of aged MPs in soil and their potential risk of groundwater contamination.

Impact of the surrounding environment on antibiotic resistance genes carried by microplastics in mangroves

The pollution of antibiotic resistance genes (ARGs) carried by microplastics (MPs) is a growing concern. Mangroves are located at the intersection of land and sea and are seriously affected by MP pollution. However, few studies have systematic research evaluating the transmission risk of ARGs carried by MPs in mangroves. We conducted in situ experiments by burying five different MPs (polypropylene, high-density polyethylene, polystyrene, polyethylene glycol terephthalate, and polycaprolactone particles) in mangroves with different surrounding environments. A total of 10 genes in the MPs of mangroves were detected using quantitative real-time polymerase chain reactions, including eight ARGs and two mobile genetic elements (MGEs). The abundance of ARGs in Guanhai park mangroves in living areas (GH) was higher than that of Gaoqiao mangroves in protected areas (GQ) and Beiyue dike mangroves in aquaculture pond areas (BY). Pathogenic bacteria, such as Acinetobacter, Bacillus, and Vibrio were found on the MP surfaces of the mangroves. The number of ARGs carried by multiple drug-resistant bacteria in the GH mangroves was greater than that in the GQ and BY mangroves. Moreover, the ARGs carried by MPs in GH mangroves had the highest potential transmission risk by horizontal gene transfer. Sociometric and environmental factors were the main drivers shaping the distribution characteristics of ARGs and MGEs. Polypropylene and high-density polyethylene particles are preferred substrates for obtaining diffuse ARGs. This study investigated the drivers of ARGs in the MPs of mangroves and provided essential guidance on the use and handling of plastics.

Comment on the paper 'Soil microplastic pollution under different land uses in tropics, southwestern China'

Research on soil microplastics is currently at an early stage, and there is no widely approved sampling protocol. Even so, any basic research should minimize errors to ensure that they are not amplified in future research. This paper examines some weaknesses of the original research paper 'Soil microplastic pollution under different land uses in tropics, southwestern China' recently published in this journal. The authors neglected to report the equipment used for soil sampling and did not use field blank samples. There is also a soil layer that was incorrectly named. The type and pore size of filter paper used for filtration during pre-analytical soil sample preparation is very important. In this paper the nature of the filter paper used, and its larger pore sizes are questionable by today's scientists. In addition, the authors in the original paper also overlooked reporting the statistical package used for statical analysis and ensuring if all data sets obey normality, homogeneity, and equality before running the one-way ANOVA test. This statistical step is widely considered mandatory, especially in the soil science community. So, this makes it difficult to trust the results documented. Furthermore, in the original paper, the needle and stereo microscope instruments used to sort microplastic-like materials prior to proper analysis are not reliable.

Microplastic effects on soil system parameters: a meta-analysis study

Microplastics are generally considered as an emerging contaminant in the environment due to their toxic additives and transport of other contaminants. However, the potential threats of microplastics in soil should be concerned due to inconsistent research results. In this study, a meta-analysis based on 32 recent relevant studies was conducted to compare the response of soil system parameters including microbial community, aggregate structure, soil nutrient contents, and crop growth to the presence of microplastics. The results showed that microplastics presented no significant effects on soil dissolved organic carbon contents and the amounts of available phosphate, nitrate, and ammonium. Although microplastics would not significantly influence the diversity of soil microorganisms, they could significantly increase soil microorganism amounts with a standard mean difference at 19.32. We also found that microplastics tended to significantly decrease soil water stable macro-aggregate (> 0.25 mm) contents with a significantly negative standard mean difference (- 0.90) in meta-analysis. Moreover, soil microplastics seemed not to affect crop growth by having non-significant effects on both crop under-ground and above-ground biomasses. These results indicate that up to date, the main negative impacts caused by microplastics on soil systems could be their negative functions on soil aggregation.